Electrostatic discharge guide and liquid crystal display utilizing same

ABSTRACT

An electrostatic discharge guide comprises a ground wire isolated from a data line. The ground wire has a main ground segment and at least one electrostatic discharge triggering segment connected to the main ground segment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a liquid crystal displaywith an electrostatic discharge guide, and more particularly to a liquidcrystal display with a structure guiding electrostatic discharge tooccur at a specific location.

2. Description of the Related Art

Electrostatic discharge, abbreviated as ESD in the followingdescription, may occur during measurement, assembly, installation, anduse in integrated circuits and liquid crystal displays and may damagethe circuits or devices therein. Furthermore, function of the entiresystem may be affected. The three models often explain the causes of ESDstress. The first ESD stress model of the Human Body Model (HBM) refersto ESD stress caused by discharge when a charged human body touches adevice under test (DUT). The second ESD stress model of the MachineModel (MM) refers to ESD stress caused by discharge when a chargedmachine contacts a device under test (DUT). The third ESD stress modelof the Charged Device Model (CDM) refers to ESD stress caused bydischarge when a charged DUT contacts a conductor which is at adifferent voltage potential.

In the fabrication process of a thin film transistor liquid crystaldisplay (TFT-LCD), a panel is processed by many machines and operators.Inevitably, electrostatic charge builds up. Electrostatic charge that isnot released in some way is harmful to the TFT-LCD. Typically, the Jouleheat generated during discharge causes ESD damage to a TFT-LCD. Jouleheat may result in a short circuit between two isolated conductors or anopen circuit caused by melted conductive wire. Both types of damage maycause the TFT LCD to malfunction.

Damage can be detected by electrical testing subsequent to fabricationof a liquid crystal display. However, TFT-LCD is large devices measuredin inches while the physical dimensions of ESD damage is measured inmicrometers. Thus rapid determination of location of ESD damage in alarge size display and rapid repair thereof are important issues.Overcoming either or both issues can enhance the repair rate and improveyield.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a structure for guidingelectrostatic discharge to a specific location.

Thus, the present invention provides an ESD guide comprising a groundwire, isolated from a data line, with at least one main ground segmentand at least one electrostatic discharge triggering segment connected tothe main ground segment.

According to an embodiment of the present invention, the electrostaticdischarge triggering segment comprises two ends connected with the mainground segment respectively.

In another embodiment of the present invention, the ground wire furthercomprises an opening substantially surrounded by the main ground segmentand the electrostatic discharge triggering segment and intersecting thedata line.

According to another embodiment of the present invention, theelectrostatic discharge triggering segment has a first line width andthe main ground segment has a second line width. The first line width issmaller than the second line width.

The present invention provides another liquid crystal display with anelectrostatic discharge guide. The liquid crystal display comprises asubstrate, a plurality of data lines arranged substantially in parallelthereon, and at least one ground wire isolated from and intersecting thedata lines to form a plurality of intersecting regions. In eachintersecting region, the ground wire comprises at least one main groundsegment isolated from and intersecting a corresponding data line and atleast an ESD triggering segment, connected to the main ground segment,isolated from a corresponding data line.

In the liquid crystal display with an ESD guide, the ground wires arelocated between the substrate and each data line or each data line islocated between the substrate and the ground wire.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description in conjunction with the examples andreferences made to the accompanying drawings, wherein:

FIG. 1 illustrates the electrostatic discharge guide with the data linelocated under the ground wire;

FIG. 2 illustrates a short circuit between a data line and a ground wirewhen ESD occurs in the electrostatic discharge guide shown in FIG. 1;

FIG. 3 illustrates the method for repairing the short circuit shown inFIG. 2;

FIG. 4 illustrates an open circuit of a data line when ESD occurs in theelectrostatic discharge guide shown in FIG. 1;

FIG. 5A illustrates a repairing method wherein a repair wire circumventsa defect;

FIG. 5B illustrates a repairing method wherein a repair wire crosses adefect;

FIG. 6 is a liquid crystal display according to the present invention;and

FIG. 7 illustrates an electrostatic discharge guide with twoelectrostatic discharge triggering segments.

DETAILED DESCRIPTION OF THE INVENTION

Electrostatic discharge typically occurs at a location where currentdensity is higher and results in an open or short circuit of a dataline. To prevent open or short circuits caused by electrostaticdischarge at the intersection of a data line and a ground wire, thepresent invention provides a structure for guiding electrostaticdischarge to occur at a specific location. The structure is useful forthe repair of data lines and ground wires.

FIG. 6 shows a TFT-LCD according to one embodiment of the presentinvention. The TFT-LCD comprises a substrate 60, a ground wire GND anddata lines DL₀˜DL_(N-1). Data lines DL₀˜DL_(N-1) are implementedsubstantially in parallel on the substrate 60. A ground wire GND is alsoimplemented on the substrate 60. From the three dimensional viewpoint,the sequence of the layers are substrate 60, ground wire GND, and datalines DL₀˜DL_(N-1). The sequence may alternately be substrate 60, datalines DL₀˜DL_(N-1), and ground wire GND.

Ground wire GND and data lines DL₀˜DL_(N-1) are isolated and intersectedto form a plurality of intersections 62 ₀˜62 _(N-1). All intersectionsare identical. To simplify the description, the structure of theintersection 62 ₀ is given as an example. The scope of the invention,however, is not limited by the following explanation.

Referring to FIG. 1, a data line DL₀ is located under a ground wire GNDand they are electrically isolated from each other. The ground wire GNDhas a main ground segment 72 and one electrostatic discharge triggeringsegment 70 at the intersection of the ground wire GND and the data lineDL₀. Both ends of the electrostatic discharge triggering segment 70 areconnected with the main ground segment 72. Both ends of theelectrostatic discharge triggering segment 70 are connected with themain ground segment 72 and are therefore regarded as part of the groundwire GND. The electrostatic discharge triggering segment 70, the mainground segment 72 and the surrounding area form an opening 10 at theintersection of the ground wire GND and the data line DL₀.

It is noted that in FIG. 1, the line width of the electrostaticdischarge triggering segment 70 is smaller than that of the main groundsegment 72. The main advantage of such design is that the ESD currentflows through the electrostatic discharge triggering segment 70 insteadof the main ground segment 72 when an ESD event discharges through thedata line DL₀ and the ground wire GND. The method is described in thefollowing.

It is well known that at the equal potential surface of a conductor, theintensity of electric field is directly proportional to the curvature ofthe surface. Put simply, on the same conductor, the electric fieldincreases with the curvature. Once ESD stress occurs across the dataline DL₀ and the ground wire GND, breakdown starts from theelectrostatic discharge triggering segment 70 because the electric fieldis higher at the electrostatic discharge triggering segment 70 than atthe main ground segment 72. In other words, if there is a first ESDtriggering voltage at the electrostatic discharge triggering segment 70and a second ESD triggering voltage at the main ground segment 72 inFIG. 1, the first ESD triggering voltage is obviously lower than thesecond ESD triggering voltage. Therefore, the electrostatic discharge isguided to occur at the intersection of the narrower electrostaticdischarge triggering segment 70 and the data line DL₀. Thus, the ESDcurrent flows through electrostatic discharge triggering segment 70instead of the main ground segment 72. When ESD damage to the data lineDL₀ is discovered, the damage can be verified by observing theintersection of the electrostatic discharge triggering segment 70 andthe data line DL₀.

An ESD event occurring across the data line DL₀ and the ground line GND,wherein heat is definitely generated at the intersection of theelectrostatic discharge triggering segment 70 and the data line DL₀, hasthree potential results. The first result may be a short between theelectrostatic discharge triggering segment 70 and the data line DL₀, thesecond possible result may be meltdown of the electrostatic dischargetriggering segment 70, and the third result may be meltdown of the dataline DL₀ at the intersection. Meltdown of the electrostatic dischargetriggering segment 70, however, does not result in circuit malfunctionand as such is not addressed. The repairing methods for repairing ashort circuit and a melted data line DL₀ are described in the following.

FIG. 2 shows a short between the electrostatic discharge triggeringsegment 70 and the data line DL₀ caused by ESD. The method for repairingthe short is illustrated in FIG. 3. The repair is accomplished bydisconnecting the ends B and C of the electrostatic discharge triggeringsegment 70 and the electrostatic discharge triggering segment 70 isthereby disconnected from the ground wire GND. As a result, the dataline DL₀ is isolated from the ground wire GND. A laser cut can then beutilized to cut a thinner electrostatic discharge triggering segment 70.Further, to ensure that the data line DL₀ remains normal, a repair wirecan be formed to cross over the defect A to connect both ends of thedata line. The repairing method is illustrated in detail in FIGS. 5A and5B.

FIG. 4 shows a meltdown of data line DL₀ at the intersection and an opencircuit formed at location A caused by ESD. In FIG. 4, the ground wireGND is located under the data line DL₀ and disconnected. The repairingmethod is illustrated in FIG. 5A or 5B. The method forms an additionalrepair wire 20 across the open circuit A to re-connect the data lineDL₀. Generally, two contacts 30 a and 30 b across the defect A on thedata line DL₀ are formed by a laser, i.e. contact windows 30 a and 30 bare formed in the dielectric layer on the data line DL₀. Subsequently, arepair wire 20 is formed by laser CVD. The repair wire 20 electricallycontacts the data line DL₀ via contacts 30 a and 30 b. Since the-use ofa laser to form contacts 30 a and 30 b may result in melting between thetwo layers, locations of the contacts 30 a and 30 b should not overlapthe ground wire GND. As shown in FIGS. 5A and 5B, the contact 30 bcorresponds to the opening 10 of the ground wire GND. The formed repairwire can circumvent the defect A, as shown in FIG. 5A or directly crossover the defect A, as shown in FIG. 5B. If the data line DL₀ shouldcontact with the ground wire GND when it is broken, the repair can beaccomplished by cutting the ends B and C of the electrostatic dischargetriggering segment 70. Again, a laser can be utilized to cut a narrowerelectrostatic discharge triggering segment 70.

Moreover, the number of the electrostatic discharge triggering segmentsof the ground wire intersecting the data line DL₀ can be one, two, ormore. As shown in FIG. 7, if two electrostatic discharge triggeringsegments 70 and a main ground segment 72 are desired, two openings 10,perpendicular to the data line DL₀, in the ground wire GND at theintersection are required.

The present invention provides an electrostatic discharge guide, whichdirects ESD damage to occur at specific locations. Therefore, damage canbe rapidly identified. Furthermore, the electrostatic dischargetriggering segments simplify the repair process.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. An electrostatic discharge guide device comprising: a data line; anda ground wire, comprising: at least one main ground segment, isolatedfrom and intersecting the data line; and at least one electrostaticdischarge triggering segment, connected to the main ground segment,isolated from and intersecting the data line.
 2. The electrostaticdischarge guide device as claimed in claim 1, wherein the electrostaticdischarge triggering segment comprises two ends connected to the mainground segment.
 3. The electrostatic discharge guide device as claimedin claim 1, further comprising an opening, substantially surrounded bythe main ground segment and the electrostatic discharge guide,intersecting the data line.
 4. The electrostatic discharge guide deviceas claimed in claim 3, wherein the electrostatic discharge triggeringsegment has a first line width narrower than a second line width of themain ground segment.
 5. A liquid crystal display comprising anelectrostatic discharge guide, the liquid crystal display furthercomprising: a substrate; a plurality of data lines, arrangedsubstantially in parallel on the substrate; and at least one groundwire, isolated from and intersecting the data lines to form a pluralityof intersecting regions; wherein in each intersecting region, the groundwire comprises: at least one main ground segment isolated from andintersecting a corresponding data line; and at least one ESD triggeringsegment, connected to the main ground segment, isolated from andintersecting a corresponding data line.
 6. The liquid crystal display asclaimed in claim 5, wherein both ends of the electrostatic dischargetriggering segment are connected with the main ground segment.
 7. Theliquid crystal display as claimed in claim 5, wherein in eachintersecting region, the ground wire further comprises an opening,substantially surrounded by the main ground segment and theelectrostatic discharge guide, intersecting the data line.
 8. The liquidcrystal display as claimed in claim 5, wherein the electrostaticdischarge triggering segment has a first line width narrower than asecond line width of the main ground segment.
 9. The liquid crystaldisplay as claimed in claim 5, wherein the ground wire is locatedbetween the substrate and each data line.
 10. The liquid crystal displayas claimed in claim 5, wherein each data line is located between thesubstrate and the ground wire.